1. Field
This application relates generally to methods of epitaxially growing SiC layers on single crystal SiC substrates and to semiconductor devices made using these methods.
2. Background of the Technology
Silicon carbide possesses properties that make it an excellent semiconductor material for applications that involve high temperature, high power, high radiation and/or high frequency. Properties that contribute to this superior performance are its large bandgap, excellent physical stability, high thermal conductivity, high electric breakdown field, and high saturated electron drift velocity. Semiconductor devices fabricated from SiC are capable of operating at temperatures above 600° C.
SiC occurs in many different crystal structures called polytypes. The SiC polytypes are formed by the stacking of double layers of Si and C atoms. Each double layer may be situated in one of three positions, designated as A, B, and C. The sequence of stacking determines the particular polytype. There is one cubic polytype known as 3C or β-SiC. It has a three-layer repeat sequence ABC. All of the other polytypes are known as α-SiC and have either a hexagonal or rhombohedral structure. The hexagonal 4H-SiC polytype has the four layer repeat sequence ABCB. The hexagonal 6H-SiC polytype has the six layer repeat sequence ABCACB. For the α-SiC polytypes, the (0001) plane is known as the basal plane and this plane is perpendicular to the crystallographic c-axis direction.
Epitaxial growth of SiC is disclosed in the following references: U.S. Pat. No. 7,247,513 and in References [8] and [10]. Homoepitaxial growth of α-SiC has been conducted on an off-axis surface of a substrate (i.e., a surface that is at an angle to the basal plane of the substrate). For example, U.S. Pat. Nos. 4,912,064, 5,011,549 and 5,248,385 disclose homoepitaxial growth of SiC films on 6H-SiC substrates with a non-zero off-axis angle. Other references disclosing epitaxial growth of SiC on the surfaces of substrates with a non-zero off-axis angle include: References [1], [2], [3], [4], [5], [6], [7], [9] and [11]. The use of off-axis substrates results in waste, however, due to the need to slice the single-crystal boule off-axis to the direction of crystallographic growth (i.e., the c direction). As wafer diameters increase, this can result in a significant amount of waste of the expensive single-crystal boule.
Accordingly, there still exists a need for improved methods of epitaxially growing SiC layers on substrates which is cost effective and which produces SiC layers having low defect density.